The Duality of Quantum Mechanics

 The Duality of Quantum Mechanics

 One of the most peculiar, confusing, and debatable concepts of physics that makes us question the very reality of our existence is Quantum physics.

It raises the most fundamental question for the Physicists, do the same rules of Classical physics that apply to the everyday objects we interact with apply to quantum level as well?  Nothing divulges the essence of our quantum reality as righteously as a single Experiment - The Double Slit Experiment.

The wave-particle duality of light has been a topic of debate for physicists since long.

The Double slit experiment suggests that the very act of observing a particle has a dramatic effect on its behavior.

 

To start off, imagine throwing pebbles at the wall with 2 slits in it. Some will bounce off the wall, but some will travel through the slits. If there is a screen behind the wall, the pebbles that have travelled through the slits will hit it. If you mark all the spots where a pebble has hit you would see two strips of marks roughly the same shape as the slits.

 

 

Now imagine shining a light (of a single wavelength) at the same wall with two slits.  Two slits will act as 2 different light sources and will create an interference pattern on the screen.

Now imagine the same experiment with electrons.  imagine firing electrons at the wall but block one of these slits. Some of the electrons will pass through the slit and will create a pattern on the screen just like the pebbles. Now open the second slit, you would expect 2 rectangular strips on the screen, but you see is an interference pattern from a wave. You might think the electrons are somehow interfering with each other, but even if you fire the electrons one by one so that they have no chance of interfering, the interference patterns still remains.

 

It gets weirder when you add a detector by the slits to know which slit is the electron actually going through. By doing so, the interfere patterns disappears and instead, the particle pattern of two strips. If you remove the detectors again, the interference pattern reappears.

Somehow the act of observing the electron is making electrons to change their behavior.

The experiment suggests that the electrons or any other quantum particle demonstrates both particles as well a wave like characteristics.  Th electron in the above experiment exist as a cloud of probabilities and it is the probabilities that are interfering and creating a pattern on the screen. However, the act of observation makes it collapse and forces it to choose a location in space.